Microwave transmission lines are well known in the art. These so-called waveguides include the well-known rectangularly cross sectioned hollow pipe wave guide through which radio frequency waves propagate from a source to a destination. Microwave transmission lines also include the so-called stripline and microstrip waveguides (also considered transmission lines) as well.
A microwave stripline transmission line is generally comprised of three conductors; a center conductor generally lies between two layers of dielectric material both of which lie between two outer, ground-plane conductors. A microstrip transmission line on the other hand generally consists of a layer of dielectric material between two conductive strips.
Stripline and microstrip transmission line are well known in the art. They have many specific uses but, one electronic device or circuit to another.
In many radio communications applications it is desirable to be able to split a radio frequency signal into one or more reduced amplitude signals. At high frequencies (microwave frequencies generally above 1 gigahertz Ghz.) a so-called signal splitter generally takes the form of a discrete or distributed quarter wavelength section of transmission line or waveguide in a "T" configuration. A single input port device with two output ports electrically splits an input signal into two components, one output from each of two output ports. In addition to splitting a radio frequency signal, it is frequently desirable to be able to combine two radio frequency signals at microwave frequencies, such as where the signals from one or more antennas are combined to a single input port of a radio receiver. Like splitters, prior art combiners typically employed two or more quarter wavelength sections tied together at one common point to implement such a radio frequency combiner.
A problem with prior art quarter-wavelength microwave splitters and combiners is their relatively narrow bandwidth, frequency-dependent operating characteristics. Quarter-wavelength stubs that comprise a microwave signal splitter or combiner will in fact have an electrical length of a quarter wave at substantially one frequency. If the frequency of an input signal changes appreciable from the frequency at which the electrical length of the stubs is a quarter wave long, the operating characteristics of the splitter or combiner might change appreciably.
A radio frequency splitter or combiner which has reduced frequency dependency (one that is more broad band) would be an improvement over the prior art.